A wind turbine comprises several components including a tower, a nacelle, a generator, a rotor comprising a hub and rotor blades and so on. Yaw systems are conventionally used in wind power stations to yaw the turbine nacelle to the required angle against the wind. When a wind turbine is erected, the blades, the hub, the tower and the nacelle are transported to the site of erection. The tower is erected, the nacelle is mounted on the tower, the hub is mounted on the nacelle and the rotor blades are attached to the hub by means of at least one crane. When erected on land, normally mobile cranes are used to position, orient and arrange the components relatively to each other so that the components are able to be mounted together. During this erection phase in wind turbine construction, it is also necessary to yaw the nacelle while mounting the rotor and again, post lifting, to allow the crane to track unobstructed to the next site. As in any other physical systems, faults/failures may occur in the system. Specifically, if there are any failures with the yaw system during the erection phase, costly standstills of manpower and equipment will result.
In order to operate and test the yaw and hydraulic systems, specific voltages must be supplied to the nacelle. Unfortunately, yaw failures can only be detected after the nacelle is erected on the tower because the required voltages are not available on the ground.
Wind turbines, yaw controls, and testing systems are well known in the art, including those described in US Patent and Application Nos. 2009/0100918, 2009/0016227, 2008/0266400, 2008/0307647, 2009/0004009, 2009/0039651, 2009/0129931, each of which is incorporated herein by reference.